This disclosure is related to hydronic heating and cooling applications and more specifically to software control systems for hydronic heating and cooling applications.
Identification and Significance of the Problem or Opportunity—More energy is consumed by buildings than any other segment of the U.S. economy, including transportation or industry, with almost 41% of total U.S. energy consumption devoted to taking care of our nation's home and commercial building energy needs. This is an increase from 39% in 2006, which utilized approximately 39 quadrillion Btu (quads) of energy to service the 113 million households and 74.8 billion square feet of commercial floor space in the United States. Total building primary energy consumption in 2009 was about 48% higher than consumption in 1980. Space heating, space cooling, and lighting were the dominant end uses in 2010, accounting for close to half of all energy consumed in the buildings sector.
More than $400 billion is spent each year to power homes and commercial buildings, consuming more than 70% of all electricity used in the U.S. and contributing to almost 40% of the nation's carbon dioxide emissions. The Energy Information Administration estimates that energy consumption in buildings—primarily electricity and natural gas—will exceed fifty quads in the next two decades. If the U.S. can reduce building energy use by 20%, approximately $80B would be saved annually on energy bills, and significant reduction of greenhouse gas emissions would be realized.
Next-generation building controls have the potential to produce significant energy savings in buildings. For example, annual energy consumption associated with functions addressed by conventional building controls—i.e., lighting, heating, cooling, and ventilation-totals nearly ten quads, or 57% of primary energy. These ten quads broadly frame the energy savings opportunity for building controls. Investment in energy-efficiency R&D within the buildings sector—especially in the key area of advanced controls—could significantly reduce energy consumption. However, the potential to realize these savings via innovative building controls has been hampered by several market and industry barriers.
First, R&D investment in the building industry is much lower than in many other industries. This is in part due to market fragmentation, with many actors required to construct and operate a building (e.g., manufacturers, designers, builders, subcontractors, suppliers, etc.). This limits the ability of the private sector to effectively coordinate research and reliably bring innovations to market. Moreover, building control innovations are particularly challenging to bring to this cost-sensitive market because their benefits are difficult to quantify—especially without independent verification of savings levels. Investment in building energy efficiency R&D by private companies dropped 50% between 1991 and 2003.
Development of innovative and cost-effective controls is also hampered by ownership issues of commercial and residential buildings. Building occupants who are not owners have little incentive to invest in building-efficiency improvements. The owners are also unwilling to upgrade to high-efficiency equipment and appliances because they do not see the benefit of reduced utility bills, which the occupant pays. For example, while utilities constitute only 1% of total building expenses, they account for 30% of tenant operating expenses. Peak demand charges account for 40% of commercial building electricity expenses, of which 75% of these relate to lighting and Heating, Ventilation, and Air Conditioning (HVAC) systems. Most commercial buildings are cooling dominated. Ground Source Heat Pumps (GHPs) can reduce peak demand charges by operating at one-half the peak load electrical demands of conventional equipment. When combined with hydronic high thermal mass distribution systems, GHP-centric HVAC systems have the potential to reduce tenant operating expenses over 20%. Hydronic as used herein is defined as the use of a fluid such as water as the heat-transfer medium in heating and cooling systems.
Prevailing design/bid/build paradigms also impede deployment of advanced controls, with focus on completing buildings quickly and inexpensively. Common sequential design processes make extensive use of prior design experience, resulting in a bias against innovative approaches with lower market adoption. Integrated and synergistic design of building systems is also challenged by current practices.
Finally, a central issue with installing controls to implement energy savings measures is that energy expenditures account for a small (approximately 1%) proportion of total annual building expenditures. Investment in core business activities often competes with energy-efficiency investments such as advanced controls. Building owners/operators must have very high levels of confidence that investments in building controls will have a quick payback for those investments to prove attractive. The innovation disclosed herein delivers the technology that will provide that high level of confidence.
Advanced, low-cost, “smart” building controls have the technical potential to reduce U.S. commercial building HVAC and lighting energy consumption by about one quad of primary energy annually, or roughly 6% of current total use. In addition, many offer significant peak-demand reduction potential. But as stated above, advanced building controls face first-cost and several non-economic barriers to realizing greater market penetration. The U.S. Department of Energy Building Technologies Program understands these unique technology and industry barriers to developing innovative technologies, and has requested high-risk, high-reward innovative research focused on technology that has the potential to contribute to a 50% reduction in energy demand by residential and commercial buildings at less than the cost of the energy saved (800 trillion Btu's in annual savings by 2020 and 3,000 trillion Btu's in annual savings by 2030).
As part of that “50% reduction” effort, the Department of Energy (DOE) is striving to develop and demonstrate “crosscutting, whole building technologies such as sensors and controls. These efforts support the net zero energy buildings goal not only by reducing building energy needs, but also by developing design methods and operating strategies which seamlessly incorporate solar and other renewable technologies into commercial buildings.”
Integrated hydronic heating and cooling applications have the potential to reduce the residential and commercial building energy use by 50% while increasing occupant comfort, safety, and indoor environmental quality at substantially less cost than the energy saved.
The Hydronic Building Systems Control (HBSC) described in this disclosure is a low-cost standards-compliant software-based control that integrates traditional and renewable hydronic system components for building heating, cooling, and hot water. HBSC addresses known technology gaps with a software solution, and produces a controls requirement specification that can be hosted on commodity hardware such as that developed for the smart phone market.
HBSC also addresses shortcomings of commonly used HVAC systems by removing barriers to market adoption of hydronic heating and cooling systems. Widespread use of forced air systems contributes to high healthcare costs and decreased occupant productivity caused by poor Indoor Environmental Quality (IEQ) and thermal comfort, while increasing vulnerability to terrorist attack with potential negative impact on public welfare and national security. Current hydronic system technologies, while highly energy efficient, struggle in the marketplace due to system cost, controller complexity, and retrofit difficulty. HBSC technology has the ability to overcome problems with forced air systems providing heating, cooling, and ventilation.
The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and international standards organizations mandate the use of mechanical ventilation to provide fresh air in tight buildings. For higher system energy efficiency, heat recovery is combined with the mechanical ventilation using an energy transfer and ventilation device. The heat exchange and ventilation is usually achieved with an air-to-air heat exchanger with one or more built-in fans, commonly known as a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV). In climates where heating is more prevalent than air conditioning, an HRV is used. In cooling climates, an ERV is recommended. In hot humid climates, air conditioning and/or dehumidification equipment are used in conjunction with ERVs or HRVs to enhance user comfort and indoor climate.
Within a HRV, contaminated exhaust air and fresh outside air pass through the heat recovery core in separate passages that prevent air contamination or mixture. The fresh outside air then absorbs the heat and warms up, and is distributed at a more comfortable temperature to the various rooms by the ventilation system. An HRV can help make mechanical ventilation more cost effective by reclaiming energy from exhaust airflows. HRVs use heat exchangers to heat or cool incoming fresh air, recapturing 60% to 80% of the conditioned temperatures that would otherwise be lost. Conventional fan and vent assemblies for bathrooms and kitchens, often required by building code standards for ventilation, may allow significant energy losses. An HRV system can incorporate small, separately switched booster fans in these rooms to control moisture or heat generated by activities like showering or cooking. Odors and pollutants can quickly be removed, but energy used to condition the air is recycled in the heat exchanger.
ERVs exchange moisture between the exhaust and fresh air streams. ERVs are especially recommended in climates where cooling loads place strong demands on HVAC systems. In some cases, ERVs may be suitable in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream is transferred to incoming outdoor air. However, ERVs are not dehumidifiers. While the ERV transfers moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream, the desiccant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. Mechanical vapor compression refrigeration equipment, known as air conditioners, is the most common approach utilized to reduce humidity while cooling.
Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The process is highly effective in cooling to reduce sensible and latent heat contained in the air. Sensible heat is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature. Latent heat is the quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and atmospheric pressure. A forced-air cooling system has the ability to remove sensible heat (cooling the air) and remove latent heat (through dehumidification which removes heat contained in the water vapor in the air stream). The dew point is the temperature below which the water vapor in a volume of humid air at a given constant barometric pressure will condense into liquid water at the same rate at which it evaporates. The relatively cold (below the dew point) evaporator coil condenses water vapor from the processed air (much like an ice-cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. Humans are most comfortable when 40% to 50% relative humidity is maintained in the occupied space.
A specific type of air conditioner that is used only for dehumidifying is called a dehumidifier. A dehumidifier is different from a regular air conditioner in that both the evaporator and condenser coils are placed in the same air path, and the entire unit is placed in the environment that is intended to be conditioned (in this case dehumidified), rather than requiring an external condenser coil. Having the condenser coil in the same air path as the evaporator coil produces warm, dehumidified air. The evaporator (cold) coil is placed first in the air path, dehumidifying the air exactly as a regular air conditioner does. The air next passes over the condenser coil re-warming the now dehumidified air. Note that the terms “condenser coil” and “evaporator coil” do not refer to the behavior of water in the air as it passes over each coil; instead they refer to the phases of the refrigeration cycle. Having the condenser coil in the main air path rather than in a separate, outdoor air path (as in a regular air conditioner) results in two consequences—the output air is warm rather than cold, and the unit is able to be placed anywhere in the environment to be conditioned, without a need for an external condenser.
Unlike a regular air conditioner, a dehumidifier will actually heat a room just as an electric heater that draws the same amount of power as the dehumidifier. A traditional air conditioner transfers energy out of the room by means of the condenser coil, which is outside the room. In this thermodynamic system, the room is the system and energy is transferred out of the system. Conversely with a dehumidifier, no energy is transferred out of the thermodynamic system because the dehumidifier is entirely inside the room. The power consumed by the dehumidifier is energy that is input into the thermodynamic system and remains in the room as heat energy.
Air-conditioning systems using cooling towers can promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes. Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in environments where an appropriate atmosphere is critical to occupant safety and well-being. Air conditioning can have a negative effect by drying out the air causing dry skin and negatively affecting sufferers of allergies and asthma. Air conditioning can also be used for dehumidification, as water vapor condenses on the air coil during cooling.
Specific issues associated with forced air HVAC systems include:
1. Poor Energy Performance Due To Distribution Ductwork—Poorly installed forced air residential HVAC systems often use twice the energy of a properly installed system. Duct leakage in commercial buildings accounts for 0.3 quads of annual energy consumption. In a study involving residences in Fresno, Calif., 93% of the homes had duct leakage greater than 150 cubic feet per minute. A recent audit of certified air conditioning contractors by Xcel Energy for a high efficiency rebate program in Colorado found that in 46% of the retrofit installations conducted in 2011, neither the ductwork nor the equipment was installed correctly.
2. Poor IEQ and Thermal Comfort—Prior research shows a correlation between employee productivity, IEQ, and thermal comfort. The costs attributable to these indoor climate conditions have a greater economic impact than all building operations and energy expenses combined. The dominance of worker salaries as a percentage of office building expenses is staggering, accounting for approximately 80% of expenditures in a small office building. Increasing employee productivity 2% would offset all building operations and energy expenses combined. The healthcare and legal costs associated with poor IEQ are equally formidable. For example, Legionnaire's disease can occur from the airborne dispersal of Legionella bacteria from improperly maintained cooling towers, humidifiers, and evaporative condensers. Most building owners do not acknowledge that forced air HVAC systems are causal agents to poor IEQ resulting in higher absenteeism or poor health.
3. Vulnerability to Terrorist Attack—Commercial building owners are ignorant of the terrorist risk inherent with large forced air systems. Ground-mounted HVAC equipment and the related forced air distribution systems which return air from any one zone to the entire building ventilation system are particularly vulnerable. Due to the air volume required to heat, cool, and ventilate, a typical 100 ton rated Variable Air Volume (VAV) system weighs over twenty tons and requires 5,000 cubic feet of space. A 100,000 square foot building requires four of these units. In many cases the size and weight requirements force a designer to place the units at ground level. By introducing a chemical, biological, radioactive, or nuclear agent into these systems, a terrorist could inflict mass human casualties and great psychological damage.
Although hydronic systems offer solutions to these shortcomings, they bring with them a unique set of adoption barriers, including:
1. Market Bias—While HVAC system designers have a bias toward vapor compression technology, the highest system energy efficiency is possible with the direct use of heated or cooled fluids in a hydronic distribution system (radiant floor, radiant ceiling panels, chilled beams, or hydronic fan coils). Passive cooling using chilled fluid from a Ground Source Heat Exchanger (GHEX), and passive heating using process heat or solar fluid provides the highest system energy efficiency. The system design is straightforward, and the heat transfer can be accomplished with a low energy circulator, without the need for a boiler, chiller, or GHP. However, a barrier to adoption is the lack of a commercial control appropriate for this application.
2. Perceived High First Cost—High mass radiant floor systems are perceived to have a higher first cost than ducted air systems. HVAC systems designers in the U.S. prefer forced air systems over hydronic systems, though most will acknowledge that radiant floor heating systems are more comfortable with improved IEQ to the forced-air alternative. Designers incorrectly assume these technologies are incompatible. Hydronic distribution used in conjunction with hydronic fan coils is a viable compromise, particularly with Water-to-Water (W-W) GHPs providing both hot and chilled water. An in-floor high mass radiant heating and cooling system—installed at a lower cost than a ducted air system—would be market disrupting.
3. Poor Hydronic Control Outcomes—Customers lack confidence in advanced control capabilities and the energy savings benefits of integrated renewable energy equipment, such as GHPs, for the following reasons:
a. Most conventional off-the-shelf controls are functional for one device using a few sensors. With few exceptions, such as set-back capabilities, they do not provide optimal system energy efficiency. Residential examples include separate controls for the furnace, hot water and HRV/ERV, with more pronounced energy losses and thermal discomfort issues in large commercial buildings which have even less zoning functionality.
b. Enterprise Direct Digital Controls (DDCs) are expensive to install, program and maintain. Soft costs for design, implementation, commissioning, and maintenance are substantial, often eliminating any value for controls investment. Enterprise controls may provide interoperability, yet usually do not provide higher system energy efficiency. Besides the first cost of these controls, this lack of proven performance represents the largest market barrier. DDC is complicated, proprietary and owners often feel “held hostage” by controls companies. The high soft costs associated with these controls reduce building commissioning rates to less than 5% for new construction and 0.03% of existing buildings.
c. Lowest Common Denominator Control Solutions—The HVAC industry is segmented by product. Manufacturers, suppliers, and installers are aligned to these product lines. The end result is serial control of disparate equipment with minimal consideration or expertise applied to system energy efficiency. Design professionals, builders, and HVAC contractors will require a baseline system architecture which is affordable, easy to implement, and provides seamless interoperability between legacy equipment and emerging technology.
d. Inadequate controls and equipment efficiency ratings based on steady state test conditions have created distrust by building owners toward control and equipment manufacturers who have failed to deliver on efficiency claims. Equipment efficiency ratings for heating (Coefficient Of Performance, COP) and cooling (Seasonal/Energy Efficiency Ratings, SEER/EER) published by the Air Conditioning and Heating Institute (ARI) are not substantial for predicting actual system performance. The ARI metrics are based on steady state moderate test conditions without consideration for overall system energy efficiency (Seasonal Performance Factor, SPF) affected by seasonal temperature extremes, partial load conditions, intermittent operation and HVAC distribution efficiency.
e. Hydronic distribution systems are more efficient than forced air systems. Yet commercial controls in the U.S. for hydronic applications are limited. These systems may incorporate space heating and cooling via a radiant floor, radiant ceiling, or distributed hydronic fan coils. In all of these distribution methods, the highest system energy efficiency gains are possible by controlling the operation of the heating/cooling equipment along with the supply temperature.
f. W-W ground source heat pumps are more efficient with greater functionality than boilers, yet the available GHP hydronic controls use boiler control logic. Within the U.S., the majority of W-W ground source heat pumps utilize a single stage compressor and do not require multi-stage controls. However, when a W-W GHP is equipped with a two-stage compressor, the typical control is single stage.
g. Water-to-Air (W-A) GHPs are more efficient with greater functionality than furnaces with direct exchange cooling or air source heat pumps, yet the available controls are often modified furnace/air conditioner thermostats with three levels of heating, two cooling, and a fan mode. Source circulator control as provided by the GHP manufacturer is typically a binary relay. Since the source circulators are usually contained in one “flow center,” this on-off functionality activates all of the source side circulator pumps providing sufficient flow for the rated maximum capacity of the GHP. In a residential application utilizing a GHP equipped with a two-stage compressor, the GHP operates at second stage less that 20% of the heating/cooling season. One pump in a typical two pump flow center uses 500 watts of power. If the heat pump is rated at 6 tons, two pumps are used. Yet at partial load conditions, only one pump is required. By reducing the source flow when the GHP is at partial load conditions, the system energy efficiency is increased without changing the GHP's component efficiency. The excessive energy use of these circulators under partial load conditions is not accounted for in GHP ARI ratings. In typical applications, the circulators are fixed speed. Unless the GHP or controls manufacturer provides energy efficient circulator control, the overall highest system energy efficiency—which includes the energy consumption of source side circulator pumps—is not optimum. If the manufacturer does not provide relays for multiple pumps, multiple speed pumps, or variable speed pumps control, installing contractors install the flow center with all pumps active regardless of actual flow requirements under partial load conditions. These limitations cause the GHPs to underperform with respect to advertised efficiencies derived in steady state testing. Recently, dedicated variable speed controllers are offered on board heat pumps equipped with variable speed compressors. Source side pump control is not typically available for enterprise control of multiple heat pumps. Attaining the highest system energy efficiency determines the operation of the circulator pumps. An industry acceptable flow rate for a ground or water source heat pump is 3 gallons per minute per ton of actual output. A heat pump incorporating a multi-stage or variable speed compressor does not require flow at the rated capacity, rather a flow rate which meets the actual capacity. The required flow may also be varied based on the entering water temperature to the heat pump. However, existing logic boards with the GHPs assume that source water temperature cannot be varied, so available controls do not account for water temperature variances when optimizing system energy efficiency.
4. Lost Cost Reduction Opportunities are Missed without Synergistic Design
a. High mass radiant floor heating infrastructure can use the same distribution medium for cooling. Due to a lack of capable and cost effective controls for chilled beams and Radiant Floor Cooling (RFC), building owners typically install two complete distribution systems—high mass radiant hydronic heating and ducted air system for cooling and ventilation. Radiant cooling systems use 42% less energy than comparable VAV systems (see Table 1 below).
TABLE 1Peak HVAC Energy Consumption Comparison, VAV versus Radiant Cooling% Power % Power in Itemin VAVRadiant CoolingFan And Motor37.5% 1.5%Load From Lights18.8% 9.4%Air Transport Load 9.3% 1.9%Other Loads34.4%34.4%Pumps— 1.5%Total 100%57.7%
The savings illustrated above result from the efficiencies created by hydronic distribution, increased effectiveness of radiant cooling to remove infrared heat gains from direct solar and lighting sources, and reduced air transport loads. These savings are based on using traditional chillers operating at less than one-half the efficiency of W-W GHPs. GHPs are ideal to replace boilers in Radiant Floor Heating (RFH) applications due to the lower supply temperatures required with radiant hydronic distribution. Building owners often replace inefficient boilers with condensing boilers as the first costs of GHPs do not justify an investment for heating only operations. Yet GHP equipment combined with radiant cooling architectures would decrease energy use far more than the 42.3% savings predicted above.
b. Hydronic heating and cooling systems create an opportunity to incorporate Dedicated Outdoor Air System (DOAS) or Demand Controlled Ventilation (DCV) to improve system energy efficiency, IEQ, and occupant comfort. When forced air systems are designed for ventilation and latent heat extraction only, and not the building heating and cooling sensible loads, the required air velocity and volume are greatly reduced. DOAS is a type of HVAC system that consists of two parallel systems: a dedicated outdoor air ventilation system that handles latent loads and a parallel system to handle sensible loads. DCV systems modulate outdoor intake based on carbon dioxide levels. These systems have a simple payback period of 2-5 years and the national energy savings potential of 0.3 quads.
c. Solar thermal array capacity is constrained by storage capacity. Solar thermal tanks require a higher first cost investment than solar thermal collectors. Reducing the requirement to install storage tanks to match the solar array could reduce the first cost of solar thermal arrays by 50%, while eliminating the maintenance and replacement costs for over sizing storage to meet array demands. A ground source heat exchanger is ideal to handle this excess capacity, yet GHP contractors are not familiar with design criteria for this hybrid system and lack the controls to implement a design.